A lock cylinder can have a pivotable closure which is located behind the cylinder cover and which consists of a closing flap which closes the insertion orifice of the key channel, the flap being pivotable about an axis at right angles to the longitudinal axis of the cylinder, one end of a torsion spring resting against the face of the closing flap directed towards the interior of the key channel.
Known lock cylinders of this type are difficult to assemble, especially because a torsion spring is used. A torsion spring of this type has to be tensioned when the closing flap is installed in the cylinder, and the entire unit has to be held in place during the fastening of the cylinder cover, which retains the unit as a whole. The quality of protection achieved by means of a pivotable closing flap necessitates making assembly simpler, thus allowing mass-production at a competitive price.